1. Field of the Invention
The present invention relates to a zoom lens that is appropriately used in, for example, a video camera, a digital still camera, and a portable information terminal (PDA: Personal Digital Assistance) and an imaging apparatus including the same.
2. Description of the Related Art
In recent years, in an imaging apparatus, such as a digital still camera, with a reduction in the size of an imaging device, such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), there is a demand for reducing the overall size of the apparatus. It is preferable that the total length of the lens be reduced and the overall size of the lens system be reduced in order to reduce the overall size of the imaging apparatus.
JP-A-2001-350093, JP-A-2003-255228, and Japanese Patent No. 3391342 disclose a four-group-type zoom lens in which four lens groups with positive, negative, positive, and positive refractive powers or positive, negative, positive, and negative lens groups are arranged in this order from an object side, or a five-group-type zoom lens in which five lens groups with positive, negative, positive, negative, and positive refractive powers are arranged in this order from the object side. In order to obtain a high zoom ratio, the five-group-type zoom lens is more advantageous than the four-group-type zoom lens. In this case, it is preferable to sufficiently reduce the total length of the lens or variation in aberration when power varies.
JP-A-2001-350093 discloses a zoom lens that satisfies the following conditions:1.1<f1/ft<2.5
(where f1 indicates the focal length of the first lens group and ft indicates the focal length of the entire system at a telephoto end).
When the above-mentioned conditions are satisfied, the focal length f1 of the first lens group with respect to the focal length ft at the telephoto end is long. Therefore, the total length of the lens increases, which is disadvantageous in reducing the size of the zoom lens.
JP-A-2003-255228 discloses a five-group-type zoom lens in which five lens groups with positive, negative, positive, negative, and positive refractive powers are arranged in this order from the object side and the fourth lens group includes one lens. In this structure, since the fourth lens group includes one lens, there is a large variation in aberration when power varies. In addition, when the fourth lens group is moved during focusing, there is also a large variation in aberration during focusing.
Japanese Patent No. 3391342 discloses a zoom lens that includes a first lens group with a positive refractive power, a second lens group with a negative refractive power, a third lens group with a positive refractive power, and at least one subsequent group which are arranged in this order from the object side. In the zoom lens, the first lens group has a total of three or less lenses including at least one negative lens and at least one positive lens, and the refractive index Nd and the Abbe number vd of the at least one positive lens with respect to the d-line satisfy the following conditions:Nd<1.53; andvd>78.
However, in the conditions, since the refractive index is small, the Petzval sum increases and field curvature at the telephoto end increases. In addition, the positive lens has strong curvature, and it is necessary to increase the thickness of the positive lens, which is disadvantageous in reducing the size of the zoom lens. Since the Abbe number is large, this structure is advantageous in correcting longitudinal chromatic aberration, but is disadvantageous in correcting lateral chromatic aberration.